1. Field of the Invention
The present invention relates generally to a machine tools such as punch presses and laser processing machines and more particularly pertains to clamping apparatus for clamping materials to be processed such as sheet materials in machine tools, e.g., punch presses, laser processing machines and drilling machines.
2. Description of the Prior Art
The prior art concerning the present invention will be described, by way of example, about what is called a turret punch press which has turrets for holding a number of tools to process sheet materials such as sheet metals, although the present invention is applicable not only to punch presses other than turret punch presses but also to other machine tools such as laser processing machines.
As is well known, the turret punch press is used to punch a number of holes on sheet materials such as sheet metals as its name implies, and it is also used to form a variety of shapes such as flanges and louvers on sheet materials or form or bend sheet materials into shapes. The turret punch press comprises a vertically movable ram and a pair of rotatable upper and lower turrets for holding a plurality of upper and lower tools which are varied in size and shape to punch and form a variety of holes and shapes in sheet materials such as sheet metals. The upper and lower turrets are vertically spaced from each other substantially beneath the ram and horizontally disposed on their respective shafts which are vertically disposed so as to coaxially align with each other. Each of the upper tools on the upper turret is so located as to vertically align with either of the lower tools on the lower turret to cooperate with each other to punch holes of a peculiar shape or form shapes of a peculiar configuration. Also, the upper and lower turrets are so arranged as to be simultaneously rotated by power to bring a desired pair of the upper and lower tools into a position just beneath the ram so as to enable them to be worked by the ram to punch holes of a desired shape or form shapes of a desired configuration. In this arrangement, a workpiece such as a sheet metal to be punched and/or formed is horizontally fed by a plurality (usually a pair) of clamping means into a position between the upper and lower turrets, namely the upper and lower tools which have been placed just beneath the ram by the upper and lower turrets. The clamping means are so arranged as to grip an end of the workpiece and be moved by power in all directions toward and away from the upper and lower turrets to bring any portion of the workpiece into a position between a desired pair of the upper and lower tools beneath the ram. Also, in order to automatically and continuously punch and form a number of holes and shapes varied in size and shape in the workpiece, the upper and lower turrets and the clamping means are so arranged as to be rotated and moved under a numerical control which is preprogrammed.
In the conventional turret punch press of the above described arrangement, it has been disadvantageous that the clamping means for clamping the workpiece will often inevitably go into collision with any of the lower tools on the lower turret. The clamping means will collide with any of the lower tools when it is moving in the proximity of the upper and lower turrets to place just beneath the ram a portion of the workpiece close to the clamped end thereof. Since the clamping means is moved by power at high speed, the clamping means and the lower tools will suffer from great shock which will shorten their lives and decrease the punching accuracy, when they collide with each other. Accordingly, it has been desired to decrease the shock which is caused by the collision of the clamping means and the lower tools especially in order to move the clamping means at higher speed to perform operations at higher speed.
As another conventional disadvantage with regard to the turret punch press, workpieces such as sheet metals to be punched and/or formed are often originally bent or warped and also will become bent or warped upwardly away from the horizontal level when continuously punched and/or punched to have a number of holes and/or shapes punched and/or formed. Accordingly, it has been desired that the clamping means cope with the bends or warps of workpieces being punched and/or formed in order to perform accurate punching and/or forming operations without hurting the workpieces.
As a further conventional disadvantage with regard to the turret punch press, the clamping means has been so arranged that clamping members can move to grip the workpiece to be punched and/or formed only along the feeding level where the workpiece is to be fed into between the upper and lower turrets. In fact, the end of the workpiece which is to be gripped by the clamping members will bend down more or less lower than the feeding level, since the workpiece is of a thin sheet material. Therefore, the clamping means in the conventional turret punch press cannot moderately grip the workpiece, and the clamping means and workpiece will be often hurted.
A further conventional disadvantage with regard to the turret punch press has been that the clamping means will be pulled or pushed by the workpiece or suffer from shock caused by side thrust force especially when forming operations are being performed by the upper and lower tools to form shapes such as flanges and louvers. The side thrust force will occur especially when forming operations are being performed, since in forming operations the workpiece is placed aslant on the lower tool. Of course, the shock caused by the side thrust force will shorten the life of the clamping means and also will decrease the processing accuracy of the turret punch press.